AUSTIN (KXAN) — Austin Police’s Cold Case unit has 170 open cases, according to APD Sgt. Matthew Sanders, who supervises four cold case detectives and two missing persons detectives.

“We are looking and discussing ways to make this more efficient and consistent. But every case is unique so having a set criteria is not possible either,” Sanders said.

Xiaojia “Grace” Chen, an Austin teacher murdered in 2014. Her case is still unsolved. (File Photo)

Sanders, who took over command of the unit last month, says that cases are moved to his unit when the investigating detective retires or is promoted.

When cold case detectives investigate a case, such as the 2015 homicide of Lewis Lane, Sanders says that they start at the beginning.

“They are trying to keep themselves from being affected by biases that might have affected the original investigators,” Sanders said.

For some cases, such as the murder of Debra Sue Reiding, details are sparse:

“On Jan. 22, 1979, Robert Reiding arrived home from work and discovered the body of his wife, Debra, an 18-year-old female. He found her in bed, under the covers, with a pillow over her head. Since there was not a phone in their apartment, Robert went to a pay phone nearby and called the police.”

In a case like this, Sanders says that an investigator would first determine the “timelines and victim habits” before moving through the rest of the case.

“It can depend on what information is still available to the investigator. Every case is different,” Sanders said.

Modern investigators have access to new technologies (primarily DNA processing) that their predecessors didn’t, but even still the closure rate is slow. According to Sanders, some years no cold cases are closed, but in 1983 the unit closed 11 cold cases.

Austin’s oldest unsolved case? An 1880s serial killer known as the Servant Girl Annihilator and the Midnight Assassin, who killed eight Austin residents. Some, Austin’s ghost tour guides in particular, believe that this killer fled to England and became Jack the Ripper.

However, this case is no longer on APD’s records, Sanders said.

“We don’t have files back that far. It would be fascinating read if they were,” Sanders said.

The old case in APD’s records is the murder of Cellars Ford, which occurred on December 1,1946.

If you have information about a cold case, contact the APD Homicide tip line at 512-477-3588, Crimestoppers at 512-472-8477 or by email.